With respect to a circuit board for making up or mounting electronic parts, such as packaged LSIs such as BGA and CSP, MCM, and other integrated circuit devices, it is generally necessary to inspect the electrical properties of the circuit board before the electronic parts are assembled or mounted for the purpose of confirming that a wiring pattern of the circuit board has the expected performance.
As a method for performing electrical inspection of a circuit board, there has heretofore been known a method making combined use of an inspection electrode device, in which a plurality of inspection electrodes are arranged according to positions of lattice points located vertically and laterally, and an adaptor for electrically connecting the inspection electrodes of this inspection electrode device to electrodes to be inspected of a circuit board that is an object of inspection, or the like. The adaptor used in this method is composed of a printed wiring board called a pitch-changing board.
As this adaptor, are known that having, on one surface thereof, a plurality of connecting electrodes arranged in accordance with a pattern corresponding to electrodes to be inspected of a circuit board, which is an object of inspection, and, on the other surface, a plurality of terminal electrodes arranged at positions of lattice points of the same pitch as inspection electrodes of an inspection electrode device, that having, on one surface thereof, plural pairs of connecting electrodes each composed of a connecting electrode for current supply and a connecting electrode for voltage measurement and arranged in accordance with a pattern corresponding to electrodes to be inspected of a circuit board, which is an object of inspection, and, on the other surface, a plurality of terminal electrodes arranged at positions of lattice points of the same pitch as inspection electrodes of an inspection electrode device, and the like. The former adaptor is used in, for example, an open short-circuit test of each circuit in a circuit board, and the latter adaptor is used in an electric resistance-measuring test of each circuit in a circuit board.
In order to achieve stable electrical connection of the circuit board, which is the object of inspection, to the adaptor in the electrical inspection of the circuit board, it is generally conducted to cause an anisotropically conductive elastomer sheet to intervene between the circuit board, which is the object of inspection, and the adaptor.
This anisotropically conductive elastomer sheet is a sheet exhibiting conductivity only in its thickness-wise direction or having a great number of pressure-sensitive conductive conductor parts exhibiting conductivity only in the thickness-wise direction when they are pressurized.
Those of various structures have heretofore been known as such anisotropically conductive elastomer sheets. For example, Patent Art. 1 discloses an anisotropically conductive elastomer sheet (hereinafter also referred to as “dispersion type anisotropically conductive sheet”) with conductive particles exhibiting magnetism contained in a state that the conductive particles have been oriented in an elastic polymeric substance so as to align in a thickness-wise direction of the sheet to form chains, and in a state that the chains formed of the conductive particles have been dispersed in a plane direction of the sheet, Patent Art. 2 discloses an anisotropically conductive elastomer sheet (hereinafter also referred to as “uneven distribution type anisotropically conductive sheet”) obtained by unevenly distributing conductive particles exhibiting magnetism in an elastomer, thereby forming a great number of conductive path-forming parts each extending in a thickness-wise direction of the sheet and an insulating part mutually insulating them, and Patent Art. 3 discloses an uneven distribution type anisotropically conductive sheet with a difference in level defined between the surface of each conductive path-forming part and an insulating part.
These anisotropically conductive elastomer sheets are obtained by, for example, subjecting a molding material layer with conductive particles exhibiting magnetism contained in a liquid polymeric substance-forming material, which will become an elastic polymeric substance by being cured, to a curing treatment while or after a magnetic field is applied to the molding material layer in a thickness-wise direction thereof. In such an anisotropically conductive elastomer sheet, the conductive particles are contained in the base material composed of the elastic polymeric substance in a state oriented so as to align in the thickness-wise direction to form chains, and a conductive path by a chain formed of the conductive particles is formed by pressurizing the sheet in the thickness-wise direction.
When the dispersion type anisotropically conductive sheet is compared with the uneven distribution type anisotropically conductive sheet, the dispersion type anisotropically conductive sheet has the advantage compared with the uneven distribution type anisotropically conductive sheet in that the dispersion type anisotropically conductive sheet can be produced at low cost without using a special and expensive mold and can be used irrespective of the pattern of electrodes to be connected and thus has general-purpose property.
On the other hand, in the uneven distribution type anisotropically conductive sheet, the insulating part mutually insulating adjacent conductive path-forming parts is formed between the adjacent conductive path-forming parts, so that the uneven distribution type anisotropically conductive sheet has the advantage of having performance that electrical connection to respective electrodes can be achieved in a state that necessary insulating property has been secured between adjacent electrodes even about an object of connection, in which a clearance between adjacent electrodes is small, i.e., having high resolving power compared with the dispersion type anisotropically conductive sheet.
In order to improve resolving power in the dispersion type anisotropically conductive sheet, it is essential to make the thickness of the dispersion type anisotropically conductive sheet small.
However, an anisotropically conductive elastomer sheet having a small thickness involves a problem that performance that variations of height in respective electrodes to be connected can be absorbed to achieve electrical connection to the electrodes, i.e., irregularity-absorbing ability is low. More specifically, the irregularity-absorbing ability of an anisotropically conductive elastomer sheet is about 20% of the thickness of the anisotropically conductive elastomer sheet. For example, in an anisotropically conductive elastomer sheet having a thickness of 100 μm, stable electrical connection can be achieved even to an object of connection, in which variations of height in electrodes are about 20 μm. In an anisotropically conductive elastomer sheet having a thickness of 50 μm, it is however difficult to achieve stable electrical connection to an object of connection, in which variations of height in electrodes exceed 10 μm.
In order to solve such a problem, there has been proposed an anisotropically conductive connector composed of a composite conductive sheet including an insulating sheet and tapered movable conductors fitted to tapered through-holes formed in the insulating sheet and provided in the through-holes movably in a thickness-wise direction of the insulating sheet, and two anisotropically conductive elastomer sheets respectively arranged on both surfaces of the composite conductive sheet. (see, for example, Patent Art. 4).
According to the anisotropically conductive connector having such a composite conductive sheet, the movable electrodes in the composite conductive sheet are provided movably in the thickness-wise direction of the sheet, so that the two anisotropically conductive elastomer sheets arranged respectively on one surface and the other surface of the composite conductive sheet are compressed and deformed interlockingly with each other when pressurized in the thickness-wise direction, and so the total of the irregularity-absorbing abilities possessed by both elastomer sheets is developed as the irregularity-absorbing ability of the anisotropically conductive connector. Accordingly, high irregularity-absorbing ability can be achieved.
It is only necessary to secure the thickness required to achieve necessary irregularity-absorbing ability by the total thickness of the two anisotropically conductive elastomer sheets, so that anisotropically conductive elastomer sheets having a small thickness may be used as the respective anisotropically conductive elastomer sheets, and so high resolving power can be achieved.
However, the above-described anisotropically conductive connector actually involves the following problems.
In the anisotropically conductive connector as above, the movable conductors in the composite conductive sheet are supported by both insulating sheet and anisotropically conductive elastomer sheets, and the movable conductors may possibly fall off from the insulating sheet when the composite conductive sheet is separated from the anisotropically conductive elastomer sheets, so that it is actually extremely difficult to handle the composite conductive sheet by itself. Accordingly, when trouble occurs on one of the composite conductive sheet and the anisotropically conductive elastomer sheets in the anisotropically conductive connector, only the composite conductive sheet or anisotropically conductive elastomer sheet cannot be replaced by new one, and the whole anisotropically conductive connector must be replaced by new one.
The movable conductors of the composite conductive sheet are obtained by depositing a metal in each of the tapered through-holes formed in the insulating sheet by a plating treatment to form a metal body and mechanically pressing this metal body, thereby separating the metal body adhered to the inner surface of the through-hole. However, when an anisotropically conductive connector having a great number of movable conductors is produced, it is difficult to surely separate all metal bodies formed in the insulating sheet from the respective inner surfaces of the insulating sheet, so that inconvenience is caused to the function of a part of the movable conductors.    Patent Art. 1: Japanese Patent Application Laid-Open No. 93393/1976;    Patent Art. 2: Japanese Patent Application Laid-Open No. 147772/1978;    Patent Art. 3: Japanese Patent Application Laid-Open No. 250906/1986;    Patent Art. 4: Japanese Patent Application Laid-Open No. 2001-351702.